问题描述
我不熟悉使用Data Reader,我需要以下代码的帮助,我想从数据库中检索单个数据.
I'm not familiar with using Data Reader, i need help with the following code, i want to retrieve a single data from the database.
MySqlDataAdapter data = new MySqlDataAdapter(cmd);
conn.Open();
DataTable dt = new DataTable();
data.Fill(dt);
gridView1.DataSource = dt;
int retrievedValue = 0;
using (MySqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
if ((int)reader["order_status"] == 0)
{
retrievedValue = (int)reader.GetValue(0);
GridView View2 = sender as GridView;
e.Appearance.BackColor = Color.Green;
e.Appearance.BackColor2 = Color.ForestGreen;
}
}
}
推荐答案
reader["order_status"]
返回object
,因为您已经告知它是一个已经整数,所以需要将其强制转换为int
首先.
reader["order_status"]
returns object
, since you told it is an already integer, you need to cast it to int
first.
您还需要使用 ==
运算符,因为它是一个相等运算符. =
运算符是赋值运算符.
You need to use ==
operator as well since it is a equality operator. =
operator is an assignment operator.
if ((int)reader["order_status"] == 0)
或者您可以使用 GetInt32
方法及其基于从零开始的列号.假设它是查询返回的第一列,您可以像这样使用它;
Or you can use GetInt32
method with it's zero-based column number. Let's say it's the first column that your query returns, you can use it like;
if(reader.GetInt32(0) == 0)
顺便说一句,如果您只想获得单个值,我强烈怀疑您可能想使用 ExecuteScalar
方法,因为它位于第一行的第一列.然后,您可以将查询构造为SELECT order_status FROM ...
等.
By the way, if you wanna get only single value, I strongly suspect you may wanna use ExecuteScalar
method since it get's the first column of the first row. Then you can structure your query as SELECT order_status FROM ...
etc..
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